Energy

1. Energy • Energy is the potential to do work. Energy • can be converted from one form to another • but can not be created or destroyed. • Units (Nutrition) • calorie is most often used in US = heat • required to raise the temperature of 1 g • of water from 16.5 to 17.50 C. • 1 calorie = 4.184 joules • 1 kcal = 1,000 calories • 1 Mcal = 1,000 kcal

2. Energy • Gross energy = Energy (E) in the feed measured in a calorimeter • Digestible energy (DE) = E in the feed - E in • the feces. • Measured in digestion trials • Metabolizable energy (ME) = E in the • feed - (E in the feces + E in urine + E in combustible gases) • Measured in digestion studies + collect • gas loss

3. Energy • Retained energy (RE) = ME - heat loss (HE) • Measured in • 1) Calorimeter study • Measure energy intake and energy • losses • 2) Comparative slaughter experiment • Measure energy intake and energy • retained in gain

4. Energy • Metabolizable energy used for: • 1) Maintenance (heat loss) • 2) Production (gain in body mass, milk, • reproduction, wool) • Feed values • HE at zero feed intake is energy required for • maintenance • Feed intake when RE = 0 is feed required for • maintenance (Im) • NEm = HE/Im NEg = RE/(I-IM)

5. Energy + RE, 0 Mcal _ NEg Nm Maintenance ME intake, Mcal

6. Energy Value ofBody Reserves Energy mobilized, Mcal = 9.4*kg mobilized fat + 5.7*kg mobilized protein During mobilization 1 Mcal of RE = 0.80 Mcal diet NEm During repletion 1 Mcal of NEm = 1 Mcal of RE

7. Equations to EstimateEnergy Requirementsof Beef Cattle Maintenance NEm, Mcal/d = 0.077SBW.75 SBW = Shrunk body wt, kg

8. Equations to EstimateEnergy Requirementsof Beef Cattle • Adjustments in maintenance requirement: • 20% greater for Holstein • Steers and heifers similar • 15% greater for bulls • 20% greater for lactating cows • Similar for all ages • Effect of previous temperature • Effect of activity on pasture

9. Energy Required forMaintenance Effects of environmental temperature: Zone of thermal neutrality: Animal does not have to expend energy to maintain body temperature.

10. Energy Required forMaintenance • Lower critical temperature: Temperature at • which animal begins to use energy to • maintain body temperature. • Affected by hair coat, hide thickness, hair • coat dry or wet, body condition • Upper critical temperature: Temperature at • which animal begins to use energy to • maintain body temperature. • Affected by hair coat color, body condition

11. Equations to EstimateEnergy Requirementsof Beef Cattle For ration formulation RE is estimated from quantity of feed remaining after accounting for feed needed for maintenance.

13. Plant Cell • PROTEIN • SUGARS • STARCH • PECTINS • FATS CELL CONTENTS PRIMARY WALL SECONDARY WALL CROSS SECTION

14. Inside NEUTRAL DETERGENT FIBER (NDF) SECONDARY WALL HEMICELLULOSE LIGNIN ACID DETERGENT FIBER (ADF) CELLULOSE PRIMARY WALL OUTSIDE

15. Forage ADF and Dry Matter Digestibility Adapted from Miller et al. (1991)

16. Inside NEUTRAL DETERGENT FIBER (NDF) SECONDARY WALL HEMICELLULOSE LIGNIN ACID DETERGENT FIBER (ADF) CELLULOSE PRIMARY WALL OUTSIDE

17. Forage NDF and Dry Matter Intake Adapted from Mertens (1985) & Burns et al. (1997)